This invention relates to an exhaust control device for engines and more particularly to an improved exhaust control valve for improving performance and an arrangement for employing such a valve in a vehicle such as a motorcycle and a structure for protecting and cooling the valve.
It is well known that the configuration of the exhaust system for an internal combustion engine can significantly affect its performance. It has been the practice to tune the exhaust systems so that they will provide optimum performance at certain desired running conditions. For example, it has been proposed to emply an arrangement for multiple cylinder engines wherein individual exhaust pipes from the engine exhaust ports all merge into a common expansion chamber before discharge to the atmosphere. Such an arrangement has been found to significantly improve high speed performance. However, the same system has been found to produce less than desired mid-range performance because the exhaust gases from one of the exhaust pipes adversely affect the flow of exhaust gases from the ports of other of the exhaust pipes under less than full throttle condition. The reason for this is that pressure pulses are caused to be developed in the exhaust pipes that actually block the flow of exhaust gases from the cylinders under less than full range performance.
As disclosed in the copending applications entitled "Exhaust Gas Control Means for Engine", Serial No. 22,660 and 22,732, filed Mar. 6, 1987 in the name of Tadashi Sakuri et al., and assigned to the assignee of this application, there are disclosed arrangements that employ valves in the exhaust pipes for blocking these pulsations from interfering with the flow of exhaust gases. As a result, it is possible to tune the exhaust system for maximum performance and also to insure against a dip in the performance curve at mid-ranges by employing such a valve. Although this arrangement will improve this performance, the use of an exhaust control valve of this type may present some difficulties.
For example, the exhaust control valves as shown in those applications include a valve member that is movable between an opened position and a closed position for improving the performance depending upon the engine running condition. However, even when the valve is in its fully opened position, the valve member extends across the portion of the exhaust pipe that communicates with the expansion chamber and thus offers flow resistance. Such an arrangement can reduce the maximum power output of the engine.
It is, therefore, a principal object of this invention to provide an improved exhaust control valve for an engine exhaust system that will improve mid-range performance and which will not interfere with high speed performance.
It is a further object of this invention to provide an improved exhaust control valve wherein the valve member does not occupy any portion of the exhaust pipe when the valve is in its opened position.
In addition to the flow resistance problems aforedescribed, there is also some difficulty when a butterfly-type throttle valve is employed and in which the throttle valve shaft extends across the exhaust pipe. The valve shaft itself will act to obstruct the flow through the exhaust passage and thus present the disadvantages described above. In addition, the exhaust valve shaft is directly exposed to the exhaust gases and will become highly heated. As a result of this heating, there can be difficulties arise in connection with the operation of the valve.
It is, therefore, another principal object of this invention to provide an improved valve for exhaust control where the valve shaft is not disposed in the flow of exhaust gases so it will not be heated.
Engines having exhaust systems with exhaust control valves are frequently employed in motor vehicles. For example, motorcycles are a prime application for an engine having an exhaust system of this type since it is desirable to provide good performance for the motorcycle under all running conditions. In a motorcycle, the exhaust system normally comprises exhaust pipes that extend from the engine exhaust ports and a muffler that discharges the exhaust gases to the atmosphere. If an exhaust control valve is employed for improving mid-range performance, the exhaust control valve is normally supported in a cantilevered fashion from the engine exhaust ports. As a result of this and due to the relatively heavy weight of the exhaust control valve, damage to the exhaust system may result.
It is, therefore, another principal object of this invention to provide an improved exhaust system for a vehicle such as a motorcycle and which employs a control valve.
It is a further object of this invention to provide an improved arrangement for suspending an exhaust control valve of a vehicle.
As has been noted, it is practice to employ an expansion chamber for multiple cylinder engines with all of the exhaust pipes merging into a common expansion chamber. Furthermore, the expansion chamber normally communicates with the atmosphere through an exhaust pipes are merged into a common expansion chamber and a control valve is provided in this expansion chamber, it is important to insure that the flow of exhaust gases through the control valve body expansion chamber and discharge is smooth and regular. If the outlet from the expansion chamber is offset, as is commonly required with motorcycles, the placement of the individual exhaust pipes and their communication with the valve body can give rise to flow restrictions.
It is, therefore, another principal object of this invetion to provide an improved control valve arrangement for a multiple cylinder engine wherein a smooth flow is provided through the exhaust valve and expansion chamber.
It is a further object of this invention to provide an exhaust control valve for multiple cylinder engines wherein the flow is uniform through the exhaust pipes of the individual cylinders and unobstructed through the exhaust control valve.
As a specific example of a motorcycle exhaust system employing an exhaust control valve and a multiple cylinder engine, it is the practice to position the control valve beneath the engine transmission assembly. For simplicity, it is desirable to employ a single muffler and this muffler is normally positioned at one side of the motorcycle. Therefore, there are problems as aforenoted in obtaining equal flow through the exhaust pipes and smooth flow through the exhaust system.
It is, therefore, another object of this invention to provide an improved exhaust system for a multiple cylinder motorcycle engine.
As noted above, the exhaust control valve is normally provided in an area at a low position in a motorcycle, for example, under the engine transmission assembly. The exhaust control valve employs a mechanism for operating the valve and this is normally positioned externally of the valve body. As a result, the actuating mechanism is disposed in an area where it might become damaged. Although the system can be protected by enclosing it, then the heating of the components becomes a problem.
It is, therefore, yet another principal object of this invention to provide an improved arrangement for controlling the exhaust gases in a vehicle such as a motor cycle and also for cooling the exhaust control device and protecting it.